Early Posting

Accepted papers to appear in an upcoming issue

Optica Publishing Group posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

HE1,1 Mode Excited Surface Plasmon Resonance for High-Sensitivity Sensing by Photonic Crystal Fibers

Yanshu Zeng, Jingwei Lv, Haihao Fu, Xianwen Wu, Lin Yang, Wei Liu, Zao Yi, Qiang Liu, Chunjie Hu, Yan Lv, Paul Chu, and Chao Liu

DOI: 10.1364/JOSAA.474692 Received 07 Sep 2022; Accepted 18 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: Surface plasmon resonance (SPR) is widely used in photonic crystal fiber sensors. In this work, a photonic crystal fiber sensor based on HE1,1 mode excited SPR is designed and analyzed by the finite element method (FEM). The maximum wavelength sensitivity, optimal resolution, and amplitude sensitivity of the optical fiber sensor are 24,600 nm/RIU, 4.07×10-6 RIU, and 1164.13 nm/RIU, respectively for the refractive index range between 1.29 and 1.39. The sensor has excellent properties and wide application prospects in bimolecular and biochemical sensing, environmental monitoring, food safety, and other fields.

Unsupervised learning with physics-based autoencoder for estimating thickness and mixing ratio of pigments

Ryuta Shitomi, Mayuka Tsuji, Yuki Fujimura, Takuya Funatomi, Yasuhiro Mukaigawa, Tetsuro Morimoto, Takeshi Oishi, Jun Takamatsu, and Katsushi Ikeuchi

DOI: 10.1364/JOSAA.472775 Received 08 Aug 2022; Accepted 18 Nov 2022; Posted 23 Nov 2022  View: PDF

Abstract: Layered surface objects represented by decorated tomb murals and watercolors are indanger of deterioration and damage. For these dangers, it is necessary to analyze the pigments’thickness and mixing ratio and record the current status. This paper proposes an unsupervisedautoencoder model for the thickness and mixing ratio estimation. The input of our autoencoderis spectral data of layered surface objects. Our autoencoder is unique in that the decoder partuses a physical model, the Kubelka-Munk model. Since we use the Kubelka-Munk model forthe decoder, latent variables in the middle layer can be interpretable as pigments thickness andmixing ratio. We conducted a quantitative evaluation using synthetic data and confirmed thatour autoencoder provides a highly accurate estimation. We measured an object with layeredsurface pigments for a qualitative evaluation and confirmed that our method is valid in an actualenvironment. We also presented the superiority of our unsupervised autoencoder over supervisedlearning.

Coherent mode decomposition of multiple quantum well light emission

Quang Nguyen, Kevin Liang, Tanya Malhotra, Anurag Tyagi, Jim Bonar, and Nickolas Vamivakas

DOI: 10.1364/JOSAA.473368 Received 16 Aug 2022; Accepted 15 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: Developing a richer understanding of the various properties of light is central tothe field of photonics. One oft neglected degree of freedom is the second-order correlation ofthe light field, known as the coherence. In order to make proper use of this DOF, one needs tofirst obtain information about the field’s coherence, which may be characterized through thecross spectral density function, or CSD. We present a measurement of the CSD of the ubiquitous,partially coherent source that is the multiple quantum well device in its near-field region, where aphotonic structure would commonly encounter the emitted field. We show a departure from thecoherence area that is expected from an incoherent source and demonstrate the application of thecoherent mode decomposition as a way to further analyze the measured results.

Reduced inverse Born series: a computational study

Vadim Markel and John Schotland

DOI: 10.1364/JOSAA.473683 Received 23 Aug 2022; Accepted 15 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: We investigate the inverse scattering problem for scalar waves. We report conditions under which theterms in the inverse Born series cancel in pairs, leaving only one term at each order. We refer to theresulting expansion as the reduced inverse Born series. The reduced series can also be derived from anonperturbative inversion formula. Our results are illustrated by numerical simulations which comparethe performance of the reduced series to the full inverse Born series and the Newton-Kantorovich method.

Complex Wave and Phase Retrieval from A SingleOff-Axis Interferogram

GANG Luo, Yanping He, Xin Shu, Renjie Zhou, and Thierry Blu

DOI: 10.1364/JOSAA.473726 Received 25 Aug 2022; Accepted 15 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: Single-frame off-axis holographic reconstruction is promising for quantitative phase imaging. However, reconstruction accuracy and contrast are degraded by noise, frequency spectrum overlap of the interferogram,severe phase distortion, etc. In this work, we propose an iterative single-frame complex wave retrievalthat is based on an explicit model of the object and reference waves. We also develop a novel phaserestoration algorithm which does not resort to phase unwrapping. Both simulation and real experimentsdemonstrate higher accuracy and robustness compared to the state-of-the-art methods, both for the complexwave estimation, and the phase reconstruction. Importantly, the allowed bandwidth for the object wave issignificantly improved in realistic experimental conditions (similar amplitude for the object and referencewaves), which makes it attractive for large field-of-view and high-resolution imaging applications.

Comparison between Hadamard and canonical basesfor in-situ wavefront correction and the effect ofordering in compressive sensing

Pedro Quinto-Su and Dennis Scheidt

DOI: 10.1364/JOSAA.473940 Received 23 Aug 2022; Accepted 15 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: In this work we compare the Canonical and Hadamard bases for in-situ wavefront correction of a focusedGaussian beam using a spatial light modulator (SLM). The beam is perturbed with a transparent opticalelement (sparse) or a random scatterer (both prevent focusing at a single spot). The phase correctionsare implemented with different basis sizes (N = 64, 256, 1024, 4096) and the phase contribution of eachbasis element is measured with 3 step interferometry. The field is reconstructed from the complete 3Nmeasurements and the correction is implemented by projecting the conjugate phase at the SLM. Ourexperiments show that in general, the Hadamard basis measurements yield better corrections becauseevery element spans the relevant area of the SLM, reducing the noise in the interferograms. In contrast, thecanonical basis has the fundamental limitation that the area of the elements is proportional to 1/N, andrequires dimensions that are compatible with the spatial period of the grating. In the case of the randomscatterer, we were only able to get reasonable corrections with the Hadamard basis and the intensity of thecorrected spot increased monotonically with N, which is consistent with fast random changes in phaseover small spatial scales. We also explore compressive sensing with the Hadamard basis and find thatthe minimum compression ratio needed to achieve corrections with similar quality to those that use thecomplete measurements depend on the basis ordering. The best results are reached in the case of theHadamard-Walsh and cake cutting orderings. Surprisingly, in the case of the random scatterer we find thatmoderate compression ratios on the order of 10 − 20% (N = 4096) allow to recover focused spots, althoughas expected, the maximum intensities increase monotonically with the number of measurements due to thenon sparsity of the signal.

Suppression of the conjugate signal for broad-band computed imaging via synthetic phase modulation

Arturo Canales, James Zavislan, and P. Scott Carney

DOI: 10.1364/JOSAA.473089 Received 23 Aug 2022; Accepted 15 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: We present synthetic-phase modulated interferometric synthetic aperture microscopy(SPM-ISAM), a method to perform three-dimensional object reconstructions from data acquiredwith confocal broad-band interferometric microscopy (BIM) that reconstructs images virtuallyfree of coherent and depth-dependent defocus artifacts. This is achieved by implementing asinusoidal SPM method in combination with an ISAM reconstruction algorithm that uses relativelylow modulation frequencies compared to acquisition frequencies. A theoretical framework andnumerical results are provided here.

Nijboer-Zernike’s aberration theory: new computational achievements via Tchebychev’s polynomials approximation theory

Riccardo Borghi

DOI: 10.1364/JOSAA.473364 Received 17 Aug 2022; Accepted 14 Nov 2022; Posted 15 Nov 2022  View: PDF

Abstract: Nijboer-Zernike’s diffraction theory of aberration is a nearly abandoned jewel ofphysical optics. The present paper constitutes a possible attempt to extend its practical feasibility.It is found that such a task can be achieved by using what is probably the most important propertyof Tchebychev’s polynomials.

Classifying Beams Carrying Orbital Angular Momentum withMachine Learning: Tutorial

Svetlana Avramov-Zamurovic, Joel Esposito, and Charles Nelson

DOI: 10.1364/JOSAA.474611 Received 02 Sep 2022; Accepted 14 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: This tutorial discusses optical communication systems which propagate light carrying orbital angularmomentum through random media and use machine learning (a.k.a. artificial intelligence) to classify the distortedimages of the received alphabet symbols. We assume the reader is familiar with either optics or machine learning but is likely not an expert in both. We review select works on machine learning applications in various optics areaswith a focus on beams that carry orbital angular momentum. We then discuss optical experimental design including:generating Laguerre Gaussian beams; creating and characterizing optical turbulence; and engineering considerations when capturing the images at the receiver. We then provide an accessible primer on convolutional neural networks – a machine learning technique which has proven effective at image classification. We conclude with a set of bestpractices for the field; and provide example code and a benchmark dataset for researchers looking to try out thesetechniques.

Autocorrelation functions and power spectraldensities of the Stokes parameters in a polarizationspeckle pattern

Wei Wang, Steen Hanson, and Mitsuo Takeda

DOI: 10.1364/JOSAA.476171 Received 20 Sep 2022; Accepted 14 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: The concept of ensemble-average polarization and coherence has been applied to studying the fluctuating Stokesparameters in a polarization speckle observed when coherent light is passed through a birefringent polarizationscrambler. With the aid of the ensemble-average van Cittert-Zernike theorem for the propagation of ensembleaverage polar-coherence, we invesitgate the autocorrelation functions and the power spectra of the Stokesparameters to expose the dependence of the polarization-related scale-size distributions on the optical geometriesin which the polarization speckle arises. A generalized concept of the Stokes ensemble-average coherence areas isintroduced to deal with the polarization-related average areas associated with polarization speckle.

Numerical Analysis of Scattering Fields by a Multiple Plane Grating using Shadow Theory

Hideaki Wakabayashi, Masamitsu Asai, and Jiro Yamakita

DOI: 10.1364/JOSAA.475015 Received 06 Sep 2022; Accepted 14 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: In the shadow theory, a new description of electromagnetic fields using scattering factors has been employed. This paper presents a new numerical method based on scattering factors for the scattering problemof a composite dielectric grating embedded with conducting strips. The scattering factors for the primaryfields that is based on the assumption of conducting strips being removed completely and those for the secondary fields generated by the surface electric currents on conducting strips are introduced. The presentedmethod is formulated to obtain scattering factors for the total fields and Joule losses for propagating waveand evanescent wave incidences from the currents determined by using the Galerkin procedure. Numerical examples are given for an asymmetric multiple plane grating consisting of conducting strips. Thescattering properties and the normalized Joule losses are calculated for propagating wave and evanescentwave incidences. It is shown that the diffraction efficiencies and scattering factors hold the symmetries onthe reciprocity in the case of resistive plane gratings.

Measurement of spatial coherence of light

Jari Turunen, Atri Halder, Matias Koivurova, and Tero Setälä

DOI: 10.1364/JOSAA.475374 Received 13 Sep 2022; Accepted 14 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: The most frequently used experimental techniques for measuring the spatial coherence of classical light fields in space-frequency and space-time domains are reviewed and compared, with some attention to polarization effects. In addition to Young's classical two-pinhole experiment and several of its variations, we discuss methods that allow the determination of spatial coherence at higher data acquisition rates and also permit the characterization of lower-intensity light fields. These advantages are offered, in particular, by interferometric schemes that employ only beam splitters and reflective elements, and thereby also facilitate spatial coherence measurements of broadband fields.

Debye’s disguised assumptions and the conditions for validity of hisintegral representation of focused fields

Yajun Li

DOI: 10.1364/JOSAA.477104 Received 04 Oct 2022; Accepted 13 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: In the paper of Wolf and Li [Opt. Commun., 39, 205-210 (1981)], a sufficient condition wasobtained, under which the Debye integral representation (DIR, for brevity) may be expected to give agood approximation to the solution of a boundary value problem that is generally taken to represent afield in the region of focus. After a long calculation of the solid angle of the circular cone of raysover which the Debye integral extends, the validity condition of DIR reduces to the requirement thatthe Fresnel number of the diffracting aperture, when viewed from the geometrical focus, is much greatercompared to unity. The current study removes the long calculation of the cones of rays and replaces it byan analysis of Debye’s disguised assumption relating to a replacement of the actual (unknown) fieldemerging from the exit pupil by the unperturbed incident field.

Using fluorescent beads to emulate single fluorophores

Luis Aleman-Castaneda, Yi-Ting Feng, Rodrigo Gutiérrez-Cuevas, Isael Herrera-Hernandez, Thomas Brown, Sophie Brasselet, and Miguel Alonso

DOI: 10.1364/JOSAA.474837 Received 02 Sep 2022; Accepted 12 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: We study the conditions under which fluorescent beads can be used to emulate single fluorescent molecules in the calibration of optical microscopes. Although beads are widely used due to their brightness and easy manipulation, there can be notable differences between the pointspread functions (PSFs) they produce and those for single-molecule fluorophores, caused by their different emission pattern and their size. We study theoretically these differences for various scenarios, e.g. with or without polarization channel splitting, to determine the conditions underwhich the use of beads as a model for single molecules is valid. We also propose methods to model the blurring due to the size difference and compensate for it to produce PSFs that are more similar to those for single molecules.

A General Statistical Model of Irradiance fluctuations inFree Space Optics

Yousef Shishter, Rupert Young, and Falah ali

DOI: 10.1364/JOSAA.471510 Received 26 Jul 2022; Accepted 12 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: A novel model for the received irradiance statistical distribution for turbulence induced fading channels isderived. The derivation is based on expanding the extended Rytov method by associating doubly stochasticprocess to model large scale scintillation. In particular, the large scale induced fluctuations are modelled asthe product of arbitrary number of Gamma and inverse Gamma random variables, while the small scaleinduced irradiance fluctuations are modelled as a single Gamma random variable. Closed form expressionsfor the probability density function (pdf), cumulative distributions (cdf), and moment generating function(mgf) are given. Also, a procedure is proposed for associating the pdf parameters with the large and smallscales induced variances. The proposed model is seen to contain many previously published models, suchas the Gamma-Gamma (GG), and the Fischer-Snedicor F as special cases. Moreover, two new fadingdistributions are introduced and analysed, and plots for the proposed pdfs are generated and comparedwith often used models and measurements, thus showing the accuracies of the derived models.

Generation of volumetrically full Poincaré beams

Andy Black and Robert Boyd

DOI: 10.1364/JOSAA.473363 Received 17 Aug 2022; Accepted 11 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: Optical communications, remote sensing, particle trapping, and high-resolutionimaging are a few research areas that benefit from new techniques to generate structured light.We present a new method of generating polarization-structured laser beams that contain both fulland partial polarization states. We demonstrate this method by generating an optical beam thatcontains every state of partial and full polarization. We refer to this beam as a volumetricallyfull Poincaré beam to distinguish it from full-Poincaré beams, which contain all states of fullpolarization only. In contrast to methods relying upon spatial coherence to generate polarization14 structured beams with partial polarization, our method creates well-collimated beams by relyingupon temporal coherence.

Tikhonov regularization based extendedKalman filter technique for robust andaccurate reconstruction in diffuse opticaltomography

Jie Zhang, Limin Zhang, Zongyang Liu, Yanqi Zhang, dongyuan liu, Mengyu Jia, and Feng Gao

DOI: 10.1364/JOSAA.476795 Received 04 Oct 2022; Accepted 09 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: Diffuse optical tomography (DOT) is a non-invasive imaging modality that usesnear infrared light to probe the optical properties of tissue. In the conventionally-useddeterministic methods for the DOT inversion, the measurement errors were not taken intoaccount, resulting in unsatisfactory noise robustness, and consequently affects the DOT imagereconstruction quality. In order to overcome this defect, an extended Kalman filtering (EKF)based DOT reconstruction algorithm was introduced firstly, which improved the reconstructionresults by incorporating priori information and measurement errors to the model. Furtherly, tomitigate the instability caused by the ill-condition of the observation matrix in tomographicimaging problem, a new estimation algorithm was derived by incorporating Tikhonovregularization to extended Kalman filtering method. To verify the effectiveness of the EKF algorithm and Tikhonov regularization-based EKF algorithm for DOT imaging, a series of numerical simulations and phantom experiments were conducted and the experimental resultswere quantitatively evaluated and compared with two conventionally-used deterministicmethods involving algebraic reconstruction technique and Levenberg-Marquardt algorithm.The results show that the two EKF-based algorithms can accurately estimate the location and size of the target, and the imaging accuracy and noise robustness are obviously improved.Furthermore, the Tikhonov regularization-based EKF obtained optimal parameter estimations,especially under the circumstance of low absorption contrast (1.2) and high noise level (10%).

Diffraction of Gaussian and Laguerre-Gauss beams froma circular aperture using the moment expansion method

Kevin Dupraz, Aurelien Martens, Jean-Marcel Rax, and Fabian Zomer

DOI: 10.1364/JOSAA.470148 Received 11 Jul 2022; Accepted 07 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: A method based on the distribution theory is introducedto compute the Fresnel diffraction integral. It is applied to the diffraction of Gaussian and Laguerre-Gaussbeams by a circular aperture. Expressions of the diffracting field are recast into perturbation series describingthe near and far field regions.

Physical Optics Simulations for Synchrotron Radiation Sources

Oleg Chubar, Garth Williams, Yuan Gao, Ruizi Li, and Lonny Berman

DOI: 10.1364/JOSAA.473367 Received 16 Aug 2022; Accepted 07 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: We describe approaches to high-accuracy physical optics calculations used for development of X-ray beamlines at synchrotron radiation sources, as well as simulation of experiments and processing of experimental data at some of these beamlines. A special attention is paid to the treatment of partial coherence of X-rays – the topic of high practical importance for modern low-emittance high-brightness synchrotron radiation facilities. The approaches are based, to large extent, on the works of Emil Wolf and co-authors, including the basic scalar diffraction theory and the coherent mode decomposition method. The presented simulation examples are related to the case of the Coherent Diffractive Imaging beamline that is currently under development at the National Synchrotron Light Source II in Brookhaven National Laboratory.

Analytical solution of the vector radiative transfer equation for single scattered radiance: erratum

Philipp Hank, Andre Liemert, and Alwin Kienle

DOI: 10.1364/JOSAA.479016 Received 02 Nov 2022; Accepted 06 Nov 2022; Posted 09 Nov 2022  View: PDF

Abstract: Unfortunately, we have discovered a small error in our recently published work J. Opt. Soc. Am. A 39, 2045-2053 (2022) [1], which we would like to correct in this erratum. The error is located in section 2.D and affects the solution for polydisperse distributions.

Numerical simulation of phase-optimized light beams in two-dimensional scattering media

Felix Ott, Niklas Fritzsche, and Alwin Kienle

DOI: 10.1364/JOSAA.474318 Received 29 Aug 2022; Accepted 06 Nov 2022; Posted 07 Nov 2022  View: PDF

Abstract: Manipulating the incident wavefront in biomedical applications to enhance the penetration depth and energy delivery in scattering media such as biological tissue has gained alot of attention in recent years. However, focusing inside scattering media and examining theelectromagnetic field inside the medium still is an elaborate task. This is where electromagneticfield simulations that model the wavefront shaping process can help to understand how thefocal near field evolves at different depths. Here we use a two-step beam synthesis methodto simulate the scattering of complex incident wavefronts by well-characterized media. The approach uses plane wave electromagnetic near-field solutions in combination with an angular spectrum approach to model different light beams. We apply this approach to various two dimensional scattering media and investigate the focus intensity over depth while scanning withand without phase optimization. We find that the scanned non-optimized beams have two regionscharacterized by exponential decays. The absolute progression of the focus intensity over depthfor phase-optimized beams using all channels can be described by solutions of the radiativetransfer theory. Furthermore, the average enhancement factor over depth of the phase-optimizedfocus intensity compared to that without optimization is investigated for different numerical apertures and scattering media. Our results show that albeit the incident beam is diffusively scattered, the theoretical enhancement for a large number of optimization channels cannot be reached due to correlations between the channels. An increase in focus depth and an increase inthe numerical aperture reduces the difference between the expected theoretical and simulatedenhancement factors.

Optical Goos–Hänchen effect in uniaxially strainedgraphene

Dariush Jahani, omid akhavan, Aamir Hayat, and Muzamil Shah

DOI: 10.1364/JOSAA.475224 Received 08 Sep 2022; Accepted 06 Nov 2022; Posted 08 Nov 2022  View: PDF

Abstract: We prove the existence of relatively large Goos–Hänchen(GH) shifts for graphene in the presence of an appliedstrain in different crystallographic directions for p and spolarized beams. It is shown that GH shifts are smoothlyincreased by stretching the graphene’s lattice. Moreover,we investigate GH effect for strained graphene as a function of the Fermi energy which could be controlled byexternal factors such as gate voltage. We show that applied strain along zigzag and armchair orientations givesdifferent results for GH shifts which could provide aproper tool for the detection of strain in graphene.

2π ambiguity-free digital holography method forstepped phase imaging

Duo Zhang, Li Tuo, Wenxiu Lei, qian zhang, shuai wang, and Jun Dong

DOI: 10.1364/JOSAA.476200 Received 20 Sep 2022; Accepted 05 Nov 2022; Posted 07 Nov 2022  View: PDF

Abstract: It is known that phase ambiguity is always an inherent problem in digital holography. In this paper, a 2π ambiguityfree digital holography method is proposed. The method naturally avoids phase ambiguity by a quasi-analytic method.This quasi-analytic method accurately calculates the true phase by constructing an equation and solving the solutionof the equation. Thus, the inherent wrapping problem in digital holography is eliminated. For example, ourexperimental result shows that the true phase of the stepped specimen with phase distributed in [0,16π] can beobtained unambiguously. Since the proposed method naturally avoids the phase ambiguity problem, it may bebeneficial to enlarge the application potential of the digital holography. The effectiveness and accuracy of the proposedmethod are verified by both numerical simulations and experimental results.

Devising genuine cross-spectral densities by randomization of coherent fields.

Mikhail Charnotskii

DOI: 10.1364/JOSAA.473365 Received 16 Aug 2022; Accepted 02 Nov 2022; Posted 04 Nov 2022  View: PDF

Abstract: We propose a concept of devising the authentic Cross Spectral Densities (CSD) of partially-coherent beam waves by averaging the second moment of a coherent field over a certain number of random parameters. Several novel CSD examples created by randomization are presented. We discuss application of randomization to generation of the Twisted Schell Model Gaussian (TGSM) beams, and show that compound randomization leads to a new, more general class of twisted beams. We revisit the necessary non-negative definiteness condition of [Opt. Lett. 34 1399 (2009)], and show that the two-dimensional space of parameters is not necessary.

New Dual Views of the Generalized Degree of Purity

Avik Bhattacharya, Subhadip Dey, Alejandro C. Frery, and Jose Gil

DOI: 10.1364/JOSAA.476423 Received 23 Sep 2022; Accepted 01 Nov 2022; Posted 04 Nov 2022  View: PDF

Abstract: Several approaches and descriptors have been proposed to characterize the purity of coherency or density matrices describing physical states, including the polarimetric purity of 2D and 3D partially polarized waves. This work introduces two new interpretations of the degree of purity: one derived from statistics and another from algebra. In the first one, the degree purity is expressed in terms of the mean and standard deviation of the eigenvalue spectrum of the density or coherency matrix of the corresponding state. The second one expresses the purity in terms of two specific measures obtained by decomposing the coherency matrix as a sum of traceless symmetric, anti-symmetric and scalar matrices. These two approaches offer better insights into the purity measure. Furthermore, interesting relations with existing quantities in polarization optics are described.

Comparative Analysis of Speckle-based Single-Pixel Imaging Using Uniform and Non-Redundant Optical Phased Arrays

Taichiro Fukui, Kento Komatsu, Yoshiaki Nakano, and Takuo Tanemura

DOI: 10.1364/JOSAA.476683 Received 27 Sep 2022; Accepted 31 Oct 2022; Posted 02 Nov 2022  View: PDF

Abstract: Optical phased array (OPA) is a compact high-speed wavefront modulation device,which is promising for the next-generation optical sensing systems. In particular, speckle-basedsingle-pixel imaging (SSPI) using OPA is an attractive scheme since precise tuning of opticalphases is unnecessary. In this work, we present a comprehensive analysis of SSPI using anOPA with 𝑁 phase shifters by comparing two classes of OPAs: uniformly spaced OPA (UOPA)and non-redundant OPA (NROPA). Through the singular-value decomposition analysis of theillumination patterns generated from the OPA, we clarify the theoretical limit of the imagingresolution for each case. As a result, the number of resolvable points can be as large as 𝑁2 − 𝑁 + 1for the case of NROPA. This is in clear contrast to the case of UOPA, where the numberof resolvable points can only be as large as 2𝑁 − 1. Finally, imaging results of a test targetare compared to study the impact of the array layout in OPA-based SSPI. Our work providestheoretical understanding of OPA-based SSPI and reveals the effectiveness of SSPI using NROPA.

ULD-Net:3D Unsupervised Learning by Dense Similarity Learning with Equivariant-Crop

yu tian, da song, mengna yang, jie liu, GUOHUA Geng, mingquan zhou, kang li, and Xin Cao

DOI: 10.1364/JOSAA.473657 Received 18 Aug 2022; Accepted 27 Oct 2022; Posted 01 Nov 2022  View: PDF

Abstract: Though many recent deep learning methods have achieved good performance in point cloud analysis, most of them are built upon the heavy cost of manual labeling. Unsupervised representation learning methods have attracted increasing attention due to their high label efficiency. How to learn more useful representations from unlabeled 3D point clouds is still a challenging problem. Addressing this problem, we propose a novel unsupervised learning approach for point cloud analysis, named as ULD-Net, consisting of an Equivariant-Crop (Equiv-Crop) module to achieve dense similarity learning. We propose dense similarity learning that maximizes consistency across two randomly transformed global-local views at both instance level and point level. To build feature correspondence between global and local views, an Equiv-Crop is proposed to transform features from the global scope to local. Unlike previous methods that require complicated designs such as negative pairs and momentum encoders, our ULD-Net benefits from the simple Siamese network that relies solely on stop-gradient operation preventing the network from collapsing. We also utilize the feature separability constraint for more representative embeddings. Experimental results show that our ULD-Net achieves the best results of context-based unsupervised methods and comparable performances to supervised models in shape classification and segmentation tasks. On the linear SVM classification benchmark, our ULD-Net surpasses the best context-based method STRL by 1.1% overall accuracy. On tasks with fine-tuning, our ULD-Net outperforms STRL under fully-supervised and semi-supervised settings, in particular, 0.1% accuracy gain on ModelNet40 classification benchmark, and 0.6% mIoU gain on ShapeNet Part segmentation benchmark.

Implementing a non-4f relay system for Hartmann-Shack wavefront sensing

Charlie Börjeson, Dmitry Romashchenko, Peter Unsbo, and Linda Lundström

DOI: 10.1364/JOSAA.470047 Received 11 Jul 2022; Accepted 25 Oct 2022; Posted 25 Oct 2022  View: PDF

Abstract: Hartmann-Shack wavefront sensors (HSWSs) are used in many disciplines to measure optical aberrations. Conventionally, the wavefront of interest is transferred onto the lenslet array of the HSWS with a telescopic 4f relay system. However, the 4f relay design restricts the choice of focal lengths and distances used for the relay system. In this paper, we describe a non-4f variant and demonstrate both theoretically and experimentally that its wavefront relaying properties equal that of a 4f system. We also present an alignment method for conjugating the wavefront with the lenslet array of the HSWS for both 4f and non-4f systems.

Mathematical Modeling and Experimental Verification of Aging Human Eyes Polarization Sensitivity

Qi Wang, Peter Bryanston-Cross, Yahong Li, and Zhiying Liu

DOI: 10.1364/JOSAA.469734 Received 05 Jul 2022; Accepted 24 Oct 2022; Posted 25 Oct 2022  View: PDF

Abstract: The polarization perception sensitivity of the human eyes affects the perceivedpolarized image quality. In this study, we used polarized spatiotemporal structured images todevelop a spatiotemporal age mapping of the polarization perception of human eyes. We builtan optical Modulation Transfer Function mathematical model of the aging human eyes withspatiotemporal frequency domains and introduced the Stokes vector to analyze the polarizedimages. The proposed model provides a testing method based on a set of polarization imageswith spatiotemporal frequencies varying according to the perception of different-aged viewers.Then, we experimentally validated the proposed model by performing polarization perceptiontests on a group of volunteers. The test method has the diagnostic potential to confirm thehealth of human eyes and identify potential age-related macular diseases.

Optimal Pupil Basis Set for Telescope-CoronagraphDesign and Perturbation Analysis Based on the Methodof Moments

Su Yan, Pin Chen, Mamadou Wade, and Tepper Gill

DOI: 10.1364/JOSAA.472995 Received 11 Aug 2022; Accepted 23 Oct 2022; Posted 25 Oct 2022  View: PDF

Abstract: This paper concerns optimization and analysis of telescope-coronagraph systems for direct imaging ofexoplanets. In this paper, the coronagraph system, with arbitrary pupil geometry, is theoretically considered and the governing equation for the pupil design is derived. The method of moments (MoM) isapplied to solve the a generalized energy-concentration eigenvalue problem to obtain the optimal pupilapodization and complete sets of orthonormal basis functions for arbitrary pupil geometries. The methodyields eigenvalues indicating fraction of starlight energy encircled in the area of the focal-plane mask(FPM), where starlight can be occulted and/or nulled. In other words, higher eigenvalue implies lessleakage/spillover of light outside of the FPM region and into the planet-discovery zone. Thus, a highereigenvalue supports better starlight suppression for a given type of coronagraph. This methodology isuseful for semi-quantitatively ranking different modes of perturbation with respect to energy spillage inthe focal plane independent of coronagraph design details. A model-order-reduction-based sensitivityanalysis is conducted to investigate the coupling between different pupil modes induced by aberrations. Apupil mode recovery scheme is presented to offer a theoretically rigorous and computationally efficientapproach to reconstruct the optimal pupil mode under an arbitrary phase perturbation. The reconstructioncoefficients and recovery-effectiveness factors are derived theoretically and demonstrated numerically. Several numerical examples, including the LUVOIR A and B pupils, are provided to validate and demonstratethe applicability of the proposed methods. The reported methodology enables model-order reductionbased on degree of focal-plane energy concentration and reconstruction of optimal pupil apodizationvis-á-vis phase aberrations using a pre-computed basis set. These features should enhance computationalefficiency for coronagraph design and sensitivity analysis.

Simulating random optical fields: tutorial

Milo Hyde

DOI: 10.1364/JOSAA.465457 Received 06 Jun 2022; Accepted 22 Oct 2022; Posted 24 Oct 2022  View: PDF

Abstract: Numerous applications—including optical communications, directed energy, remotesensing, and optical tweezing—utilize the principles of statistical optics and optical coherencetheory. Simulation of these phenomena is therefore critical in the design of new technologies forthese and other such applications. For this reason, this tutorial describes how to generate randomelectromagnetic field instances or realizations consistent with a given or desired cross-spectraldensity matrix for use in wave optics simulations. This tutorial assumes that the reader hasknowledge of the fundamental principles of statistical optics and optical coherence theory. Anextensive reference list is provided, where the necessary background information can be found.We begin this tutorial with a brief summary of the coherent-modes representation and thesuperposition rule of stochastic electromagnetic fields, as these foundational ideas form the basisof all known synthesis techniques. We then present optical field expressions that apply theseconcepts, before discussing proper sampling and discretization. We finally compare and contrastcoherent-modes- and superposition-rule-based synthesis approaches, discussing the pros andcons of each. As an example, we simulate the synthesis and propagation of an electromagneticpartially coherent field from the literature. We compare simulated or sample statistics to theoryto verify that we have successfully produced the desired field and are capturing its propagationbehaviors. All computer programs, including detailed explanations of the source code, areprovided with this tutorial. We conclude with a brief summary.

1D spatially-chirped periodic structures: managing their spatial spectrum, and investigating their near-field diffraction

Mohammadreza Zarei, Davud Hebri, and Saifollah Rasouli

DOI: 10.1364/JOSAA.471764 Received 27 Jul 2022; Accepted 21 Oct 2022; Posted 25 Oct 2022  View: PDF

Abstract: This work introduces a class of 1D spatial-frequency-modulated structures, withtransmittance 𝑇 (𝑥) in which the period changes along the 𝑥 axis so that the corresponding spatialfrequency 𝑓 (𝑥) sinusoidally alternates between two values. It is shown that 𝑇 (𝑥) generally is analmost-periodic function and have an impulsive spatial spectrum. However, we find the conditionunder which 𝑇 (𝑥) is a periodic function and its spatial spectrum form a lattice of impulses. Whenthe periodicity condition is fulfilled, we call these structures as 1D spatially-chirped periodicstructures. These structures are characterized by two natural number, named as 𝑛c and 𝑛av, and areal parameter named as frequency modulation strength (FMS). As an important special case, wedefine a 1D spatially-chirped amplitude sinusoidal grating (SCASG) based on the transmissionfunction of a conventional amplitude sinusoidal grating. In which the phase of conventionalamplitude sinusoidal grating is replaced by desired chirped phase. Then the spatial spectrum of a1D SCASG is investigated by details and it is shown that the spatial spectrum can be managedby changing the value of FMS. In other words, the grating’s spectrum can be manipulated byadjusting the value of FMS. This feature might find applications in optical sharing of the incidentpower among different diffraction orders. Moreover, near-field diffraction from 1D SCASGsis studied by using so called angular (spatial) spectrum method, and Talbot distances for thesegratings are determined and verified experimentally. It is shown that the intensity profiles atquartet- and octant-Talbot distances, strongly depend on the values of the parameters 𝑛c and 𝑛av.In comparison with the conventional gratings, we see some new and interesting aspects in thediffraction from 1D SCASGs. For instance, unlike the conventional gratings, in some propagationdistances the diffraction pattern possess sharp and smooth intensity bars at which the intensity isseveral times of the incident light beam’s intensity. It is shown that the maximum intensity ofthese bright bars over the diffraction patterns depends on the characteristic parameters of thegrating, including: 𝑛c, 𝑛av, and FMS of the grating. These intensity bars might find applicationsfor trapping and aggregation of particles along straight lines.